The invention generally relates to a method for data transmission between a read/write unit and a mobile data store. More particularly, the invention relates to the use of such a method in an identification system having a read/write unit and a mobile data store.
Conventional identification systems contain at least one fixed read/write unit that contactlessly interchanges data with mobile data stores, for example, via a radio-based data transmission link. This type of system is used, for example, in technical facilities where a large number of objects or goods need to be moved as quickly as possible and with the greatest possible degree of freedom. The objects or goods can be of a wide variety of types, e.g., packages in a dispatch facility, fitting parts in a production plant, items of luggage in a transport system, etc. In this context, it is often necessary, e.g., in a production plant, to detect the type and status of the objects currently situated in physical proximity to particular locations in the facility. Further, the detection must be done quickly and unimpeded. To this end, the objects are initially provided with mobile data stores containing data which identify, for example, the type and current state of the object. Secondly, read/write units are placed at the particular locations in the facility and are frequently connected to central data processing devices.
If, for instance, a production cycle involves such objects being conveyed into the physical proximity of a selected location, then the fixed read/write unit arranged at that location can contactlessly detect the data in the mobile data stores on the objects currently situated within its respective detection range and can alter the data if necessary. A superordinate central data processing device can then be used to evaluate the data read from the data store for different purposes, e.g., to track the progress of the objects provided with the mobile data stores and, on the basis thereof, control operating systems in the respective technical facility.
An example of such a conventional identification system is described in the ISO/IEC JTC 1/SC 31 WG4 draft standard entitled “Radio-frequency Identification Standard for Item Management—Air Interface, Part 4—Parameters for Air Interface Communication at 2.45 GHz (WD 18000-4), dated Apr. 8, 2000, which is hereby incorporated by reference for all it teaches.
One notable drawback with the system disclosed in the above-mentioned draft standard, however, is that, particularly for high-speed applications such as detection and identification of railway carriages, the fastest possible processing time of approximately 15 ms is not adequate.